A Parasite That Was Once Rare in the UK — and Is No Longer
Twenty years ago, Angiostrongylus vasorum — commonly known as lungworm — was largely confined to parts of Wales and southern England. Today, cases have been confirmed across the entire UK, and the parasite is now considered endemic in many regions. Unlike gut worms, which are an inconvenience, lungworm can be fatal if it goes undetected. Every dog owner in Britain needs to understand what it is, how it spreads, and how to prevent it.
What Lungworm Is and How Dogs Get It
Angiostrongylus vasorum is a parasitic worm that lives in the pulmonary arteries and heart of infected dogs and foxes. Adult worms lay eggs that hatch into larvae, which migrate to the lungs, are coughed up, swallowed, and passed out in the faeces. These larvae are then ingested by slugs and snails, which act as intermediate hosts.
Dogs become infected by eating slugs or snails — whether deliberately or accidentally. The accidental route is more common than many owners realise. A dog does not need to eat an entire slug; larvae can transfer to grass, toys, water bowls, or even the dog's coat when slugs pass over them at night. A dog licking dewy grass first thing in the morning could be exposed.
Symptoms to Watch For
Respiratory Signs
- Persistent cough, sometimes described as a honking sound
- Exercise intolerance or breathing difficulties
- Wheezing or increased respiratory rate at rest
Neurological and Systemic Signs
- Unexplained bleeding — from wounds that will not clot, or from the nose and gums
- Seizures or disorientation
- Weight loss and general malaise
- Pale gums, indicating anaemia
The bleeding signs occur because the parasite disrupts normal clotting mechanisms, which can lead to haemorrhage in the brain, spinal cord, or internal organs. These cases can deteriorate rapidly.
Crucially, some infected dogs show very few symptoms in the early stages. By the time signs become severe, the infection may be advanced.
Diagnosing Lungworm
Lungworm cannot be detected by standard faecal worm counts. Diagnosis requires specific testing, either through a blood test that detects antigens from the adult worm, or through a Baermann technique to look for larvae in a faecal sample. Many veterinary practices can perform an in-house blood test with results available within minutes. If you suspect lungworm, ask your vet specifically about testing, as routine worming checks will not pick it up.
Treatment and What to Expect
Lungworm is treatable when caught in time. The active ingredient used is milbemycin oxime or moxidectin, both of which are available only in prescription veterinary products. Treatment typically involves a course of medication over several weeks, and dogs usually respond well if the infection has not yet caused severe organ damage.
In cases where clotting problems have developed, additional supportive treatment such as vitamin K therapy may be required. Recovery depends largely on how early treatment begins, which is why prevention is strongly preferred.
Prevention: The Most Important Section
Standard over-the-counter worming tablets do not prevent lungworm. Prevention requires a monthly prescription product containing milbemycin oxime or moxidectin, administered consistently throughout the year. Many broad-spectrum prescription treatments available from vets combine lungworm prevention with flea, tick, and gut worm control, making this straightforward to manage.
In addition to medication, practical steps help reduce exposure:
- Remove toys, bowls, and chews left outdoors overnight, as slugs cross them in the dark
- Avoid leaving water bowls outside where slugs and snails may drink from them
- Discourage your dog from eating slugs or snails during walks
- Check the garden for slug activity, particularly during wet weather
Foxes are a significant reservoir host and are common in suburban UK gardens, which is why even dogs in urban areas face real exposure risk.
Practical Summary
- Lungworm is now present across the UK and poses a genuine risk to all dogs
- Infection can occur through accidental ingestion of slugs or snail slime
- Symptoms include coughing, unexplained bleeding, and in severe cases, seizures
- Standard wormers do not protect against lungworm — a specific monthly prescription product is required
- If you suspect infection, contact your vet and ask for a lungworm-specific test
- Early treatment gives the best outcome; do not wait for symptoms to worsen